The production of LCDs typically entails manufacturing the LCDs, and subsequently testing and adjusting LCDs. During the testing and adjustment of the LCDs panels, various parameters of the LCDs are adjusted to fine tune the displaying operation of the LCDs. One such parameter, in particular, is the common electrode voltage Vcom of the LCDs. As is explained below with reference to FIG. 1, the common electrode voltage Vcom affects the display characteristics of an LCD, including the flicker characteristic.
FIG. 1 illustrates a block diagram of a typical LCD 100. The LCD 100 consists of a data signal line driver 102 to generate data voltages for pixels in common columns respectively by way of a plurality of data lines (DL#). The LCD 100 further consists of a scan signal line driver 104 to generate select line voltages for pixels in common rows respectively by way of a plurality of select lines (SL#). Each pixel 106 consists of a field effect transistor (FET) having a gate (G) electrically coupled to the corresponding select line, a drain (D) electrically coupled to the corresponding data line, and a source (S) electrically coupled to a segment electrode of a liquid crystal (LC) medium. A common electrode voltage Vcom, common to all of the pixels, is applied to a common electrode of the LC medium.
The LCD 100 further consists of a common electrode voltage adjustment circuit 108 consisting of a voltage divider including resistor R1 and variable resistor R2 connected in series between a supply voltage Vcc and ground. The intermediate node between the resistors R1 and R2 is coupled to a buffer 110 to generate the common electrode voltage Vcom.
During a frame cycle, the scan signal line driver 104 sequentially activates the select lines (SL) to respectively display the frame lines. For each activated select line (SL), the data signal line driver 102 activates the data lines (DL) depending on which pixels are to be activated based on the input image data. A pixel is activated if both the corresponding select line (SL) and corresponding data line (DL) are activated, causing the corresponding FET to turn “on”, thereby generating a current through the liquid medium (LC).
As previously discussed, the common electrode voltage Vcom affects the illumination characteristics of the pixels, such as the flicker characteristics. During testing, a technician manually adjusts the resistor R2 to set the desired common electrode voltage Vcom voltage while monitoring a test pattern displayed by the LCD. Once the desired common electrode voltage Vcom is set and all other parameters are tested and adjusted, the LCD unit is securely packaged and future access to such adjustments are not typically undertaken due to difficulties in obtaining access to such components after the LCD unit is securely packaged.
Accordingly, it is desirable to provide an interface which facilitates the electronic adjustment of such parameters. In addition, it is further desirable that such an interface include as minimal contacts for coupling to an external programming unit.